omccreary

I have a 2020 E-350 sedan.

I had a frightening incident yesterday. I was driving along a road at about 40 mph (65 kph), in normal traffic. All of a sudden my seatbelt sharply tightened – both the driver's seat and the passenger seat. Then it relaxed. It scared us.

I have no idea why. This has never happened before. Everything seemed normal before and after the incident. I drove the car another 15 miles (25 km) and nothing further happened.

Any idea what happened?

badali

There may have been a vehicle or object detected by the car that looked like an imminent collision. My car has turned on the camera system when I almost got rearended by another car. Never the seat belt tightener though...

superswiss

As said above, it does that if it detects a possible imminent collision. A car behind you might have approached rapidly and there was a chance that they might rear end you, or it could have been a false positive which while rare, it can happen.

omccreary

Thanks to you both.

I understand the principle. What about the airbag? Under what circumstances does it release the airbag? Apparently the tighten-seatbelt happens potentially more than releasing the airbag.

badali

The airbag should only release on an actual collision.

superswiss

Airbag needs an actual impact resulting in rapid deceleration.

W205C43PFL

As others mentioned, that is the MB's PRE-SAFE system working to help prepare you in case of an impact.

konigstiger

Rbt1031

The same thing happened to me and my wife the other day. No other cars or other objects nearby. Mine is at the dealer four days now with no answers. Did you ever find out the cause of your event? Mine has had numerous software updates for other faulty sensor events, in the past two years, but still does strange things (alarms, beeps, dash warnings) for no apparent reason, but this was scary for sure.

Baltistyle

Sometimes this can be caused by a reflection. It can be perceived as a brake light. I’m a bit of a speeder so get these warnings quite a bit from brake lights and it’s happened while speeding into a reflection. Did you notice if the brakes activated at all? That’s when I would worry, if there was not real event or obvious anomolistic sensor pickup. Older new tech is definitely a bit on the rough side.

S. Madman

Happened to me on my S213. And it also happened once on my W212. Multicontour seats lifted my not so ginger 300 lbs (at them time, it will probably shove me thru the pano now at 260lb) up like a gorilla lifting a baby. Was avoiding someone who was braking while getting on my lane. Seat belt tighten as well.

W205C43PFL

It is part of the Pre-Safe system, it is to prepare you for an imminent accident if the car senses that. It also does it when you do heavy braking to keep you in place, it also does it when cornering hard as well. I forgot but I think I had it do it once when I do heavy acceleration as well.

ua549

Here is an excerpt from my NTHSA complaint.

Rbt1031

I got our car back yesterday. The explanation was interesting. They basically just reinitialized the Distonic and related modules. The dealer said the system did not record any codes related to the reported seatbelt tightening problem!?
Here is tech's writeup - "Connected Battery Charger and SDS. Stored codes B223264, B1FBE29, B1FBF29, B1FC004, B223231, and B22347. Performed updates to the Multi-function camera. Multiple faults are current for the SCM module after update. Performed update to the SCM. SCM module update prompted initial startup of Distronic Control Unit. Performed initial startup of the Distronic Control Unit. Calibration Drive Required. Performed Calibration drive of the Distronic. 360 Cameras are no longer functioning after. Performed initial startup of the parking system control unit. Performed calibration drive of the 360 camera with SDS. Cleared faults and no faults returned. Original complaint is now repaired."

Baltistyle

What did this cost you and do you have a warranty? Wonder if they all need updates?

thanks

Rbt1031

My car is still under warranty, so there was no cost to me. My understanding, after talking with the service manager was the "fix" was not specific to my reported problem, but basically a reboot and initialization of the whole system. No software updates were applied or parts replaced. How they are sure it is fixed is beyond me.
This was unlike the problem I had with the rear cameras a couple of years ago (which caused alarms and the brakes to be applied by Pre-safe system in error while backing up) when it erroneously detected something behind the car. There were software updates applied then, and I never had that problem again.

superswiss

This is what they do if they don't really know what the problem is. It's basically a fresh install of the software. Just like what you do if your phone or computer acts up to the point where you don't know how to fix it other than doing a factory reset and fresh install hoping the issue was caused by corruption. I need to do this with my instrument cluster eventually as it started to keep losing some settings out of the blue.

CaliBenzDriver

That's an interesting detailed procedure.

As I understand the issue was pinned on the Steering Module gone unreliable. Other initialization steps where incidentals triggered by SCM update.

I hope software alone will help correct hardware issues created by SCM solderless connections.

I would try to be more conservative with the DistronicPlus handling of your steering/life.


SCANNER is easy...
How about you keep an eye on this mess to get $5k jobs warranted before coverage expiration....
🤞